1. Field of the Invention
The invention relates generally to position determination systems and methods, and, in particular, to systems and methods for efficiently messaging position-based data in an assisted wireless position determination system.
2. Description of the Related Art
Systems for determining the geographic position of a reference point are well known in the art. A commonly used position determination system is the Global Positioning System (GPS). GPS includes a network of Earth-orbiting satellites, spaced so that, at any given time and from any geographic position, at least four GPS satellites will be above the horizon.
In operation, each GPS satellite continually broadcasts its present position and current time. On Earth, a GPS receiver may use the information contained in these broadcast signals to compute its geographic position in terms of its longitude, latitude, and altitude. The GPS receiver typically searches for and collects the signals broadcast from four or more GPS satellites that are in view. Next, using the time interval between the broadcast time and reception time of each broadcast signal, the GPS receiver calculates the distance between the GPS receiver and each of the four or more GPS satellites. These distance measurements, along with the position and time information received in the broadcast signals, allow the GPS receiver to calculate its geographic position.
Both government regulation and consumer interest have driven the demand for geographic position functionality in wireless devices, such as wireless telephones. It is therefore desirable to introduce GPS functionality into a wireless device. However, wireless devices are extremely sensitive to network capacity and battery life considerations. Thus, adding a conventional GPS receiver to a wireless device for performing GPS functionality is an unsatisfactory solution for providing position location in the wireless device.
It is desired, therefore, to have a wireless system that provides GPS functionality to a wireless device with a minimum of additional cost to the network capacity and device battery life.
One such system for providing GPS functionality for a wireless device that minimizes the cost to the network capacity and device battery life is referred to as an “assisted wireless position determination system”. In this system, a position determination entity (PDE) is typically part of a wireless communications network that includes a plurality of base stations and at least one wireless device or mobile station (MS). In the assisted wireless position determination system, the PDE is used to aid the MS in determining its position. The system may also be based on a standard regarding the connectivity architecture of devices in a wireless communication network. One such standard is the Telecommunication Industry Association Position Determination Service Standard for Dual-Mode Spread Spectrum System-Addendum (TIA/EIA IS-801-1).
Specifically, in an embodiment of an assisted wireless position determination system, a PDE continually tracks the positions of a plurality of GPS satellites through a network of stationary GPS receivers distributed across a coverage area of a wireless communication network. Before searching for the GPS signals, an MS transmits a request for GPS aiding information to the PDE through a local base station.
The PDE, in turn, provides the MS with the aiding information, such as ephemeris data and sensitivity assistance data for the GPS satellites. For example, the PDE may use the identity of the local base station to determine an approximate location of the MS and identities and positions of the GPS satellites that are likely to be in view of the wireless device. A drawback of this system is that the data sent from the PDE to the MS may be redundant or otherwise unneeded to provide precise location information for the MS. The redundant or the unneeded data increase bandwidth requirements and time needed to fix a geographic position of the MS.
Accordingly, it is desired to provide a system and method for interconnecting devices in an assisted wireless position determination system that will reduce or eliminate redundant and/or superfluous data, thereby reducing data bandwidth requirements and improving time to fix a location of a wireless device, while still ensuring that the wireless device is not loaded with additional cost. Moreover, it is desired that such a system and method will still provide enough positioning information for the wireless device to determine precisely its geographic position.